The present invention relates to water treatment systems, sometimes commonly known as water softening systems, and more particularly to a unique water treatment tank therefore containing a packed ion-exchange resin bed.
Throughout the United States, much of the municipal or groundwater used by residential and commercial consumers alike is termed "hard" as being laden with certain mineral salts including carbonates, bicarbonates, chlorides, and sulfates of calcium, magnesium, and iron. Although generally not considered harmful through contact or ingestion, hardness in water is objectionable as the calcium, magnesium, and iron ions form insoluble soaps via a reaction with soluble soaps such as sodium stearate. Insoluble soaps, due to their sticky nature, adhere to surfaces such as bathtubs to form the dreaded "ring," and to fabrics giving them a dingy appearance. Additionally, as insoluble soaps have no cleansing power, soap in excess of that needed to precipitate the calcium and magnesium in the hard water must be added in order to obtain an adequate cleansing action. The excess soap represents an added expense to be borne by the consumer.
Hard water also is responsible for the formation of a tightly adherent scale in both boilers and teapots alike. At high temperatures, many of the minerals dissolved in hard water are precipitated as insoluble, scale-forming carbonates of magnesium, calcium, and iron, or sulfates of calcium which may foul heat exchangers, water heaters, and the like. Furthermore, a such scale has a relatively high thermal conductivity, it is a poor conductor of heat and attributes to an increased fuel consumption in boilers and water heaters and exchangers.
In view of the foregoing, it is apparent that the removal the minerals responsible for hardness in service and potable water is of economic importance both for the commercial and residential consumers. For these reasons, processes have evolved for "softening" water. In this regard, an ion-exchange process has become the most widely employed method for softening water. Ion exchange, in actuality, is a chemical reaction in which mobile, hydrated ions in solution are exchanged, equivalent for quivalent, with ions such as sodium which are of a like charge, but which form soluble precipitates with soap, carbonates, bicarbonates, chlorides, and sulfates. Naturally occurring, insoluble minerals, such as the sodium aluminosilicates known as zeolite, were the first products recognized as suitable for commercial use as ion-exchange media. The zeolite solid has an open, fishnet-like microscopic structure forming interstices which may hold, for example, mobile, positively-charged sodium cations. When water containing calcium and magnesium ions is filtered slowly in a treatment tank containing a treatment bed formed of a thick layer of coarse zeolite granules, tile calcium and magnesium in the water are replaced by the sodium in the zeolite, and vice versa, to thereby soften the water. Zeolites, however, have a relatively low ion exchange capacity per unit volume, and have been replaced by higher-capacity, synthetic resin particulates, such as polystyrene-divinylbenzene, as the ion-exchange medium of choice for water treatment tanks.
In operation, any ion-exchange resin eventually will reach the limit of its ion exchange capacity for removing magnesium or calcium ions. Thereupon, the resin must be regenerated to its sodium form with a salt or brine solution. During regeneration, the tank is taken off-line, and is first backwashed with a countercurrent flow of water to cleanse and hydraulic reclassify the resin particles in the treatment bed The resin then is regenerated with a solution of common salt, i.e., sodium chloride, which simultaneously removes the magnesium and sodium ions in the form of their soluble chlorides and replaces them with sodium ions to return the resin to its sodium-based state. The regenerated resin then is rinsed free of the soluble calcium and magnesium chloride byproducts and any excess salt and finally is returned to service ready to again soften another equal volume of hard water.
As is illustrated by Moses, U.S. Pat. No. 4,305,825, equipment for the ion-exchange process heretofore has been typified by a closed, generally cylindrical treatment tank in which the ion-exchange resin is supported on a layer of graded gravel or sand to form a treatment bed. Optionally, a layer of activated carbon for adsorbing organic compounds affecting the taste, odor, or color of the water being softened, may be included as a first treatment layer supported by the ion-exchange resin layer. A standpipe or riser tube is provided to extend from an outlet port in the top of the tank to bottom of the tank. A valve assembly also is provided to control the direction of water flow through an inlet port in the top of the tank and the outlet port at the upper end of the standpipe. The treatment tank is installed in a water line for operation under the existing water pressure, and is connected to auxiliary equipment including brine- and salt-storage tanks. In service, the valve assembly is set so that raw water to be softened is made to flow from the upper inlet port downwardly through the tank wherein it is softened as it percolates through the resin portion of the treatment bed. The treated water then flows upwardly through the standpipe where it exits the tank through the outlet port. However, as the treatment bed also exerts a filtering action of the water, the bed must be periodically backwashed effecting its expansion and suspension for removing entrained particulates which were filtered from the water during the service cycle. Such backwashing, which may be accomplished concurrently with regeneration, is effected by setting the valve assembly either to redirect the water inflow or a brine solution from an auxiliary tank through the downpipe tube. The brine or water exits the pipe at the bottom of the tank, and thereafter assumes a flow through the bed in an upward direction which is countercurrent to the downward flow during service. The backwash water or expended brine solution then exits the bed through the inlet port which is now provided by the valve assembly to be in fluid communication with a drain or sewer line.
Although representing a relatively simple and economical construction, treatment tanks of the "unpacked" type exemplified by Moses have been viewed as being of a less than optimal design. For example, the stratification of the treatment bed inevitably is disturbed as the various layers thereof, which may include activated carbon for taste and odor removal, calcium carbonate for neutralization, and manganese greensand for iron removal, are intermixed during the backwashing operation. Also, owing to a high void volume fraction within the bed, the flow of water therethrough may exhibit a channeling effect characterized by a preferential flow following the path of least resistance through the bed as opposed to a uniform or plug flow which fills the entire bed.
Indeed, as early as the year 1900, experimenters have proposed alternatives to the "unpacked" or "loose" bed design common in the water treatment art. For example, Grever, U.S. Pat. No. 661,339, offered a water filtering tank internally divided into two separate compartments by a pair of diaphragms of woven wire supported on circular grates. The compartments were filled with a filtering medium, and a flow distributor plate was provided below the inlet port to distribute the inflow equally over the filtering medium. The design was stated to eliminate the channeling effect which otherwise would have been expected to occur.
Notwithstanding that the advantages of a "packed" bed design as exemplified by Grever have been known since the turn of the 19th century, such a design has heretofore yet to be successfully incorporated into a commercially-viable water treatment tank. Rather, it has been accepted that adequate cleaning of water conditioning or softening treatment beds could be effected only by expanding and fluidizing the bed during backwashing to separate its constituent particles and allow any particulate contaminants entrained therebetween to be flushed from the bed. However, this bed expansion requires the provision of a freeboard space between the upper surface of the bed and the top of the treatment tank to accommodate the volume increase of the bed as it is expanded during backwashing. In order to provide this freeboard space during backwashing while providing for a packed bed configuration during service, Miller, U.S. Pat. No. 3,554,377, has proposed internally dividing a treatment tank into a pair of bed compartments with free-floating rather than fixed diaphragms. The diaphragms also facilitate the utilization of a stratified, multi-layered treatment bed in maintaining the segregation of the layers during service and backwash. During service, the pressure of the downwardly-directed water flow moves the free-floating diaphragms downward to compact the treatment medium. Likewise, during backwash, the pressure of the upwardly-directed water or brine moves the free-floating diaphragms upward to expand the bed compartments to accommodation the expansion of the treatment medium.
However, the Miller design suffers, as have the conventional "unpacked" bed designs heretofore common in the an, from the fact that the expansion of the bed during backwash and/or regeneration significantly increases the water usage of the tank. For example, it is not uncommon for such units to use as much as 40 to 100 gallons of water during backwash/regeneration, which at the very least lessens any water savings attributable to the use of softened water. Were water a renewable rather than a finite resource, then such usage might be considered acceptable albeit somewhat uneconomical. However, as states and municipalities have recognized the imminent need for water conservation, some have gone so far as to enacted regulations imposing maximum water usage requirements for water conditioners. Thus, it is apparent that water treatment tanks offering both water savings and improved performance are needed and would be well-received by residential and commercial users alike.